Add two or more slides to a new presentation at once

Like most programs, hold the Shift Key and click on the slides you want to add. Then drag and drop them into position in the New Presentation window. If they are in a sequence, you can click the first and last slide of that sequence, and all the slides in between will be selected.

For multiple slides, that are not in a sequence, hold the Ctrl Key and click on the slides you want to add. They will highlight in gray. Then drag and drop them into the New Presentation window.